The present invention generally relates to an electromagnetic contactor and more particularly, to a structure for fixing an electromagnetic device and a fixed point of contact within the electromagnetic contactor.
Generally, an electromagnetic contactor opens and/or closes a fixed point of contact by a movable insulative stand having a moving point of contact through a polar contact reciprocating in accordance with the excitation or de-magnetization of an electromagnetic device. Such electromagnetic contactor as referred to above is disclosed, for example, in the published specification of Japanese Patent application Laid-open Publication (unexamined) No. Tokkaisho 58-209837 (209837/1983). More specifically, in the electromagnetic contactor disclosed in this Publication No. Tokkaisho 58-209837, the fixed point of contact and the electromagnetic device are individually secured respectively to an upper casing and a lower casing which is a separate body from the upper casing. The upper casing and the lower casing have their respective faces orthogonal to a moving direction of the polar contact joined with each other so that both casings are formed into one unit in a vertical direction.
However, because of this united structure of the upper and lower casings in the vertical direction, the electromagnetic contactor is disadvantageously apt to have high possibilities for dimensional errors in the vertical direction, that is, in the moving direction of the polar contact. Therefore, the prior art electromagnetic contactor cannot get rid of a low relative positioning accuracy between internal components. It is also a problem to be solved that the contact pressure, that is, the pressure applied to a point of contact is not constant, rather is variable.
Also, in the electromagnetic contactor of the type disclosed in the Publication No. Tokkaisho 58-209837, a movable iron core (armature 7) constituting the polar contact is inserted through into a central hole (hole 17) of a spool (hoisting drum 16) so as to be able to reciprocate, which consequently restricts the position of the polar contact in the direction of the reciprocal movement.
Since the spool is thin, however, it is easily affected and deformed by contraction force at the time of molding, winding force when the coil is wound around the spool, heat stress resulting from generation of heat accompanied by application of voltage to the coil, or external force added during the operation of the electromagnetic contactor, etc. Therefore, the axial center of the movable iron core comes away from a predetermined position in the electromagnetic contactor, and the contacts are poorly overlapped with each other. Thus, the prior art electromagnetic contactor is unstable in opening-closing efficiency.
Furthermore, since the spool has a short diameter of the center hole, the reciprocal movement of the movable iron core which is restricted in position by the central hole of the spool is unreliably stable, and therefore the movable iron core is apt to waver resulting in that the contact pressure does not become constant, and the bouncing time is prolonged.